In recent years, the most of cylinder blocks of internal combustion engines have been made of a light alloy such as an aluminum alloy. In contrast with this, crankshafts are made of copper having a relatively low thermal expansion coefficient, and if bearing caps are made of a light alloy such as an aluminum alloy, bearing clearance is enlarged at warm time due to the thermal expansion difference between the crankshaft and the bearing cap, and hammering sound by combustion force occurs.
In patent documents 1 and 2, there is disclosed a configuration in which an iron-based member is inserted into each of the semi-circular concave portion of a cylinder block made of a light alloy and a bearing cap made of a light alloy to suppress the enlargement of the bearing clearance. In this configuration, the entire periphery of a main bearing part is surrounded with the iron-based member, and thereby the thermal expansion of the main bearing part is suppressed.
However, in this way, in the configuration in which the iron-based material is also inserted into the cylinder block, there are problems that an increase in the weight of the cylinder block occurs and the manufacturing process of the cylinder block becomes complicated.
An object of the present invention is to provide a bearing cap mainly made of a light alloy, which is capable of suppressing an increase in bearing clearance at warm time without a particular change in the configuration of a cylinder block made of a light alloy.